When soldering electronic components on a printed circuit board, a soldering device such as a reflow device, a jet soldering device or the like has been generally used. For example, the reflow device is provided with conveyers that convey the printed circuit board and a reflow device body to which the conveyers convey the board. An interior of the reflow device body is respectively split into a preliminary heating zone, a heating zone and a cooling zone. In the pre-heating zone and the heating zone, heaters, fans, motors for driving the fans and the like are set and in the cooling zone, cooling members, cooling fans, motors for driving the cooling fans and the like are set.
In the soldering process of the reflow device, the board which has been previously printed by the solder paste is conveyed into the reflow device. The solder paste by which the board is printed contains solder powders and the flux. The flux is obtained by dissolving solid contents such as rosin, a thixotropy agent, an activator and the like with a solvent and has an effect to remove an oxide film from a surface of metal to be soldered and to prevent reoxidation by heating at the soldering, thereby lowering surface tension of the solder to improve wettability thereof.
In the above-mentioned heating step, the flux evaporates according to the heat by heater(s) and an interior of the reflow device is filled with it. The flux thus evaporated and filled into the reflow device body is generally withdrawn and clarified through a removal device for the flux component which is arranged outside a maffle and then, it is again circulated into the maffle via a circulating circuit.
More in detail, the solder paste applied to the printed circuit board becomes flux fume by vaporizing (or evaporating) the flux component, particularly, a solvent in the preliminary heating zone. Any solid component such as rosin in the flux component melted in the preliminary heating zone, when exposed to high temperature in the heating zone, also evaporates to become fumes which float in the device (maffle). The fumes derived from these solvent and solid component are cooled and condensed when they contact relative low temperature portions, for example, conveyors for conveying the printed circuit board, fans for circulating hot air, a frame constituting the device, a labyrinth arranged in an entrance and exit or the like, in the maffle during the withdrawing step. They become solid having adhesion when they are further cooled. Any problems occur when a large amount of solid fumes, so-called fume solids is applied to each component constituting the reflow furnace.
For example, a part of the evaporated flux fumes is adhered to a surface of a member (screw shaft, nut or the like) for adjusting conveying rails for conveying the printed circuit board to be a width between the rails matching a size of the board and it becomes liquid flux fumes with flowability accompanied by reduced temperature. The liquid flux fumes are soon solidified. Since the solidified flux fumes are hard to be removed and are strongly adhered, it is not easily possible to remove them by revolving the screw shaft. Accordingly, a movement of the nut is difficult so that it is very difficult to adjust the width of the rails.
In the jet soldering device, the soldering process is performed by jetting molten solder contained in a solder bath to a surface of the printed circuit board to which the flux has been previously applied. The flux components heated by the solder layer, however, evaporate, so that the problem in the above-mentioned reflow device also occurs in the jet soldering device. In addition, even when any adhered matters are fixed to at least any one of the nut and the screw shaft other than the soldering device, any similar problems occur such that these fixed matters are not easily removed by the revolving the screw shaft.